The present invention relates to absorbent products which typically contain an absorbent core overlaid or overwrapped with a facing or cover layer.
Apertured plastic films have been used to form the covers or facing layer of absorbent articles such as disposable diapers, sanitary napkins, and dressings. The films, being hydrophobic, are not wetted with body exudates and therefore, provided the exudate passes through the apertures of the film facing, the facing will remain clean, or non-staining, and dry. One difficulty encountered in using apertured films as covers or facings on absorbent products is that body exudates do not readily flow through the apertures of the film facing into the absorbent media. Various approaches have been taken to overcome this difficulty. In one approach absorbent material such as tissue is placed in close or touching contact with the under surface of the apertured film facing to "pull" the exudate through the film. However, the use of a tissue backing can contribute to strike back, or reverse flow, from the absorbent core to the face of the cover. In addition, as tissue may be stained with body exudate, the use of tissue backing may result in the stained tissue being visible through the apertures, and staining of the aperture edge.
In the apertured film facing of the present invention the edge of the apertures is coated with a hydrophilic material to promote fluid transfer through the apertures into the absorbent core of the absorbent article. Thus the apertured film facing of the present invention provides a clean dry facing with improved liquid transfer, avoiding the disadvantages of the prior art solutions by obviating the need for a tissue backing.
Other approaches taken to enhance the fluid transfer of apertured film facings involve the careful specification of aperture size and percentage open area of the film. U.S. Pat. No. 2,992,644 discloses an absorbent dressing with an apertured film facing with a preferred apertured size of from 0.01 to 0.2 inches in equivalent hydraulic diameter and an open area of from 10 to 40%, with a preferred thickness of less than one mil. U.S. Pat. No. 4,324,246 describes an absorbent article with an apertured film facing having an open area of equal to or greater than 35%, and wherein at least 75% of the apertures have an equivalent hydraulic diameter equal to or greater than 0.025 inches, and having a thickness of less than 0.030 inches.
There are many processes for aperturing plastic film. U.S. Pat. Nos. 3,355,974, 3,719,736, 3,682,028, 3,526,349, 3,707,102 and 4,278,871 disclose processes for pin perforating plastic films. In the processes described therein, the aperture is not die cut, but is formed as the pin pierces the film, leaving a flap or flashing around the opening.
In the method of the present invention pins are used to aperture the film, and to apply a hydrophilic material to the edge of the apertures. U.S. Pat. No. 1,978,620 describes a method wherein, fibrous webs are pierced with needles, the needles dipped into a binder material, and removed from the web depositing the binder material on the web so as to bond the fibers around the formed hole.
Copending application, now U.S. Pat. No. 4,690,679 describes an absorbent product with an apertured plastic film facing made from a bi-layer film. In the aperturing process the edge of the aperture becomes formed of the plastic composition of the top, or uppermost layer.